Pyrometry filter for thermal process chamber

ABSTRACT

Embodiments of the invention generally relate to pyrometry during thermal processing of semiconductor substrates. More specifically, embodiments of the invention relate to a pyrometry filter for a thermal process chamber. In certain embodiments, the pyrometry filter selectively filters selected wavelengths of energy to improve a pyrometer measurement. The pyrometry filter may have various geometries which may affect the functionality of the pyrometry filter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/163,623, filed Jan. 24, 2014, which claims benefit of U.S.Provisional Patent Application No. 61/776,365, filed Mar. 11, 2013, bothof which are hereby incorporated by reference in their entirety.

BACKGROUND Field

Embodiments of the invention generally relate to pyrometry duringthermal processing of semiconductor substrates. More specifically,embodiments of the invention relate to a pyrometry filter for a thermalprocess chamber.

Description of the Related Art

Rapid Thermal Processing (RTP) is a well-developed technology forfabricating semiconductor integrated circuits. RTP is a process in whichthe substrate is irradiated with high intensity optical radiation in anRTP chamber to quickly heat the substrate to a relatively hightemperature to thermally activate a process in the substrate. Once thesubstrate has been thermally processed, the radiant energy is removedand the substrate cools. RTP is an energy efficient process because thechamber in which the RTP is performed is not heated to elevatedtemperature required to process the substrate. In an RTP process, onlythe substrate is heated. Thus, the processed substrate is not in thermalequilibrium with the surrounding environment, namely the chamber.

The fabrication of integrated circuits involves many steps of depositinglayers, photolithographically patterning the layers, and etching thepatterned layers. Ion implantation is used to dope active regions in thesubstrate. The fabrication sequence also includes thermal annealing ofthe substrate for many uses, such as curing implant damage andactivating dopants, crystallization, thermal oxidation and nitridation,silicidation, chemical vapor deposition (CVD), vapor phase doping, andthermal cleaning among others.

Although annealing in early stages substrate processing technologyinvolved heating multiple substrate for long periods in an annealingoven, RTP has been increasingly used to satisfy ever more stringentrequirements for processing substrates with increasingly smaller circuitfeatures. RTP is typically performed in a single substrate chamber byirradiating a substrate with light from an array of high intensity lampsdirected at the front face of the substrate on which the integratedcircuits are formed. The radiation is at least partially absorbed by thesubstrate and quickly heats the substrate to a desired high temperature.The desired temperatures generally are above 600° C. and in certainapplications, above 1000° C. The radiant heating can be quicklyactivated and deactivated to controllably heat the substrate over shorttime intervals, such as between about 60 seconds and about 1 second.

During certain processes, lower temperatures (i.e. less than 400° C.)may be required. An example of using lower temperatures includes formingsilicides on a substrate. The quality and performance of processing asubstrate in a chamber depends in part on the ability to provide andmaintain an accurate temperature of the substrate. Temperatures of asubstrate in a processing chamber are usually measured by a pyrometer,which measures temperature within a bandwidth of wavelengths. Radiationthat is within the radiation pyrometer bandwidth, and that originatesfrom the heating source, can interfere with the interpretation of thepyrometer signal if the radiation is detected by the pyrometer.“Leaking” heat radiation, radiation not intended to be measured by thepyrometer, can interfere with the pyrometer reading and provide aninaccurate temperature measurement. Moreover, not all substrates areopaque at the pyrometer bandwidth, especially when the substrate ismaintained at lower temperatures. Objects at low temperatures emitthermal radiation at lower intensity than objects at high temperatures.The weak thermal emission of low temperature objects can be overwhelmedby other heat signals and lost.

Accordingly, what is needed in the art are improved systems to measuretemperatures accurately with a pyrometer. More specifically, what isneeded is a pyrometry filter for a thermal processing chamber.

SUMMARY

Embodiments of the invention generally relate to pyrometry duringthermal processing of semiconductor substrates. More specifically,embodiments of the invention relate to a pyrometry filter for a thermalprocess chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the inventioncan be understood in detail, a more particular description of theinvention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 is a cross-sectional view of a rapid thermal processing chamberaccording to certain embodiments described herein; and

FIGS. 2A-D are cross-sectional views of a window according to variousembodiments of the invention.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements and features of oneembodiment may be beneficially incorporated in other embodiments withoutfurther recitation.

DETAILED DESCRIPTION

Embodiments of the invention generally relate to pyrometry duringthermal processing of semiconductor substrates. More specifically,embodiments of the invention relate to a pyrometry filter for a thermalprocess chamber.

Embodiments of the invention provide a thermal processing chamber forprocessing a substrate. Substrate temperature in a thermal processingchamber is often measured by radiation pyrometry. Substrate temperaturecan be determined through radiation pyrometry by measuring theemissivity of the substrate and applying known radiation laws tocalibrate a pyrometer for accurate temperature measurements. Radiationfrom a heating source (i.e. lamps) that is within the bandwidth orwavelength range of the pyrometer can interfere with the interpretationof the pyrometer signal if the interfering radiation is detected by thepyrometer. Radiation from the source may reach the pyrometer due toleakage around, or transmission through, the substrate. Such radiationmay occur during operation of the thermal processing chamber, and mayinterfere with pyrometry when the substrate is at a temperature belowabout 450° C.

FIG. 1 is a cross-sectional view of a rapid thermal processing chamberaccording to certain embodiments described herein. Further descriptionof the thermal processing chamber and instrumentation that may be usedby embodiments herein are disclosed in commonly assigned U.S. Pat. Nos.5,848,842 and 6,179,466, which are hereby incorporated by reference intheir entirety to the extent not inconsistent with the claimedinvention.

A substrate 112 to be processed in the chamber 100 is provided throughthe valve or access port 113 into the processing area 118 of the chamber100. The substrate 112 is supported on its periphery by an annular edgering 114 having an annular sloping shelf 115 contacting the corner ofthe substrate 112. A more complete description of the edge ring and itssupport function may be had by reference to U.S. Pat. No. 6,395,363,which is incorporated by reference in its entirety to the extent notinconsistent with the claimed invention. The substrate 112 is orientedsuch that processed features 116 already formed on a front surface ofthe substrate 112 face upwardly toward the process area 118. The processarea 118 is defined on its upper side by a transparent quartz window120. Although shown for schematic illustration, the features 116 on thesubstrate 112 do not generally project substantial distances beyond thesurface of the substrate 112 but constitute patterning within and nearthe plane of the surface of the substrate 112.

Three lift pins 122 may be raised and lowered to support the back sideof the substrate 112 when the substrate 112 is handled between asubstrate transfer apparatus, such as a robot blade (not shown), whichprovides the substrate 112 into the chamber 100 and onto the edge ring114. In order to heat the substrate 112, a radiant heating apparatus 124is positioned above the window 120 to direct radiant energy toward thesubstrate 112. In the chamber 100, the radiant heating apparatusincludes a large number of high-intensity tungsten-halogen lamps 126positioned in respective reflective tubes 127 arranged in a hexagonalclose-packed array above the window 120. The array of lamps 126 isgenerally referred to as the lamphead. However, other radiant heatingapparatuses may be substituted to provide radiant heat energy to thechamber 100. Generally, the lamps 126 involve resistive heating toquickly elevate, or ramp up, the temperature of the radiant source.Examples of suitable lamps include incandescent and tungsten halogenincandescent lamps having an envelope of glass or silica surrounding afilament and flash lamps which comprise an envelope of glass or silicasurrounding a gas, such as xenon and arc lamps that may comprise anenvelope of glass, ceramic, or silica that may surround a gas or vapor.Such lamps generally provide radiant heat when the gas is energized. Asprovided herein, the term lamp is intended to include lamps having anenvelope that surrounds a heat source. The “heat source” of a lamprefers to a material or element that can increase the temperature of thesubstrate, for example, a filament or gas than may be energized.

As provided herein, rapid thermal processing (RTP) refers to anapparatus of a process capable of uniformly heating a substrate at ratesof about 50° C./sec and higher, for example at rates of about 100° C. toabout 150° C./sec, and about 200° to about 400° C./sec. Typicalramp-down (cooling) rates in RTP chamber are in the range of about 80°C. to about 150° C./sec. Some processes performed in RTP chambersrequire variations in temperature across the substrate of less than afew degrees Celsius. Thus, an RTP chamber may include a lamp or othersuitable heating system and heating system control capable of heating ata rate of up to about 100° C. to about 150° C./sec, and about 200° toabout 400° C./sec.

Certain embodiments of the invention may also be applied to flashannealing. As used herein, flash annealing refers to annealing asubstrate in under 5 seconds, such as less than 1 second, and in certainembodiments, milliseconds.

In an RTP chamber, the temperature across the substrate 112 may becontrolled to a closely defined temperature that is uniform across thesubstrate 112. A passive manner of improving the efficiency includes areflector 128 extending parallel to an over an area greater than thesubstrate 112 and facing the back side of the substrate 112. Thereflector 128 efficiently reflects heat radiation emitted from thesubstrate 112 back to the substrate 112. The spacing between thesubstrate 112 and the reflector 128 may be within the range of about 3mm to about 9 mm, and the aspect ratio of the width to the thickness ofthe cavity is advantageously greater than about 20 mm. In certainembodiments, a reflector plate is applied to enhance the apparentemissivity of the substrate 112. The reflector 128, which may have agold coating or multilayer dielectric interference mirror, effectivelyform a black-body cavity at the back of the substrate 112 that functionsto distribute heat from warmer portions of the substrate 112 to coolerportions. The black-body cavity is filled with a radiation distribution,usually described in terms of a Planck distribution, corresponding tothe temperature of the substrate 112 while the radiation from the lamps126 has a distribution corresponding to the much higher temperaturesassociated with the lamps 126. The reflector 128 is disposed on awater-cooled base 153 made of a material, such as a metal, chosen forits ability to heat sink excess radiation from the substrate 112,especially during cool down. Accordingly, the process area 118 of thechamber 100 has at least two substantially parallel walls. A first wallcomprises the quartz window 120 and a second wall 153 is substantiallyparallel to the first wall. The second wall 153 may be made of amaterial that is significantly non-transparent, such as a metal.

One way of improving the uniformity includes supporting the edge ring114 on a rotatable cylinder 130 that is magnetically coupled to arotatable flange 132 positioned outside the chamber 100. A motor (notshown) rotates the flange 132 and hence rotates the substrate 112 aboutits center 134, which is also the centerline of the generally symmetricchamber 100.

Another manner of improving the uniformity divides the lamps 126 intozones arranged in a generally ring-like formation about the central axis134. Control circuitry varies the voltage delivered to the lamps 126 inthe different zones to thereby tailor the radial distribution of radiantenergy. Dynamic control of the zoned heating is affected by one or aplurality of pyrometers 140 coupled through one or more optical lightpipes 142 positioned to face the back side of the substrate 112 throughapertures in the reflector 128. The one or plurality of pyrometers 140measure the temperature across a radius of the stationary or rotatingsubstrate 112. The light pipes 142 may be formed of various structuresincluding sapphire, metal, and silica fiber. A computerized controller144 receives the outputs of the pyrometers 140 and accordingly controlsthe voltages supplied to the different rings of the lamps 126 to therebydynamically control the radiant heating intensity and pattern during theprocessing

Pyrometers generally measure light intensity in a narrow wavelengthbandwidth of, for example, about 40 nm, in a range between about 700 nmto 1000 nm. The controller 144 or other instrumentation converts thelight intensity to a temperature through the well known Planck spectraldistribution of light intensity radiating from a black-body held at thattemperature. The pyrometers 140, however, are affected by the emissivityof the portion of the substrate 112 being measured. Emissivity (c) canvary between 1 for a black-body to 0 for a perfect reflector. Thepyrometry can be improved by further including an emissometer orreflectometer to optically probe the wafer to measure the emissivity orreflectance of the portion of the wafer it is facing in the relevantwavelength range and the control algorithm within the controller 144 toinclude the measured emissivity.

As noted above, substrate temperature in the process area 118 of theprocessing chamber 100 is commonly measured by radiation pyrometry.While radiation pyrometry can be highly accurate, radiation from theheating source that is within the radiation pyrometer bandwidth mayinterfere with the pyrometer signal if this radiation is detected by thepyrometer. In RTP systems, such as those available from AppliedMaterials, Inc. Santa Clara, Calif., and other manufacturers, theinterfering bandwidth radiation may be minimized by a process kit and bythe substrate itself. The process kit couples the substrate with therotation system. The process kit generally includes a support cylinder130 and may also include a support ring, which is similar to the edgering 114.

In general, one or more pyrometers 140 may be positioned in such amanner that the substrate 112 shields the radiation source 126 from thepyrometer 140. A substrate 112 may be largely transparent to radiationfor wavelengths greater than or about 1000 nm. Accordingly, one way tolimit heat source radiation from reaching the pyrometer is to measureradiation at wavelengths at which the substrate 112 may be substantiallyopaque. For example, a silicon wafer may be substantially opaque atwavelengths less than about 1000 nm. Nevertheless, as mentioned above,the process kits can “leak” source radiation around the substrate, andnot all substrates are opaque at the pyrometer bandwidth, especiallywhen the substrate is at a temperature lower than about 450° C., such aslower than about 250° C.

One way to block the radiation originating from the radiation source 126is to prevent the source radiation in the pyrometer bandwidth fromreaching the substrate 112, for example by reflecting back to theradiation source 126. This may be accomplished by coating the window 120that separates the radiation source 126 from the processing area 118with a material that reflects the pyrometer bandwidth radiation whilepermitting sufficient source radiation for heating to pass through thewindow 120. In one embodiment, a film of reflective coating 150 may bedisposed on the side of the window 120 facing the radiation source 126.In another embodiment, a reflective coating 151 may be disposed on theside of the window 120 facing the substrate 112. In the embodiment shownin FIG. 1, a reflective coating 150 and 151 may be disposed to bothsides of the window 120. In this embodiment, the entire window 120comprises a reflective coating disposed on the surfaces of the window120 with no interruption between the reflective coating 150 and 151 andthe window 120. Further, there are no gaps or openings in the window 120that disrupt or break the continuous reflective layer 150 and 151disposed on the window 120.

By covering the window 120 with a reflective coating in the range ofwavelengths at which the pyrometer 140 is sensitive, substantially noradiation from the radiation source 126 in that range of wavelengthswill reach the substrate 112. Accordingly, when the pyrometer 140detects radiation in the range of wavelengths it is configured todetect, substantially all of the radiation measured will be from thesubstrate 112. The pyrometer 140 measurement will be subject to minimalinterference even if the substrate 112 is transparent to the pyrometerbandwidth, for example when a substrate 112 is processed below about400° C., such as about 250° C. The use of the reflective coating(s) orlayer(s) improves the measurement accuracy of the pyrometer 140.

In one embodiment, the window 120 may be removed from the chamber 100and may be coated by one or more layers of reflective material. Removingthe window 120 from the chamber 100 makes servicing of the reflectivecoating for repair or re-application of the reflective coatingrelatively easy to perform. Having the ability to remove the window isalso helpful should the window ever need to be replaced. The reflectivebehavior of the film coating depends on the materials selected and thequantity and thickness of the layers deposited. Processes and providersof services to provide windows with thin layers of reflective coatingsfor reflection in a specified range of wavelengths are known. In oneembodiment, materials used for the reflective layer may be a singlelayer, alternating layers, or any combination of high index and lowindex dielectric materials that are substantially transparent to most ofthe wavelengths of radiation emitted from the radiation source 126. Suchmaterials include, for example, titania-silica or tantala-silica. In oneembodiment, the reflective layer is made of up SiO₂ and Ta₂O₅ layers,wherein the outermost (the last deposited layer) being SiO₂. In certainembodiments, the dielectric layer film stack may include SiO₂, TiO₂,Ta₂O₅, Nb₂O₅, and combinations thereof. The ordered layering of adielectric film stack may be selected to provide desirable reflectivecharacteristics for a desired wavelength, such as a pyrometer bandwidth.

In certain embodiments, a pyrometer 140 or plurality of pyrometers areused to measure relatively low temperatures below about 400° C., such asbelow about 250° C. The pyrometer 140 detects radiation within a rangeof wavelengths of about 700-1000 nm. The range of wavelengths radiatedby the radiation source 126 in a processing chamber 100 generally rangesfrom below 700 nm to above 5.5 micron. Materials such as quartz areopaque at wavelengths above about 5.5 micron. When radiation withwavelengths between about 700-1000 nm is reflected back to the radiationsource 126, sufficient radiation of other wavelengths is still availablefrom the radiation source 126 to heat the substrate 112 to temperaturesbelow about 400° C.

FIGS. 2A-D are cross-sectional views of a window according to variousembodiments of the invention. The windows depicted in FIGS. 2A-2D maygenerally be used in the chamber 100 described in FIG. 1 or other RTPchambers using pyrometers for temperature measurement. In theembodiments depicted in FIGS. 2A-2D, the windows comprise a quartzmaterial and the reflective coatings may be selected from previouslydiscussed materials suitable for forming a reflective coating on awindow. It is also contemplated that the window may also comprisematerials other than quartz, such as alumina, yttria, glasses,aluminobariasilicate hard glass, or other substantially transparentceramics.

FIG. 2A is a cross-sectional view of a window according to oneembodiment of the invention. A window 220 for use in a thermalprocessing chamber is provided. The window 220 comprises a quartzmaterial. The window 220 comprises a top surface 216, a bottom surface218, and a peripheral region 261. In one embodiment, the top surface 216is the side of the window 220 that faces a radiation source and thebottom surface 218 is the side of the window 220 facing a processingarea. A top center region 217 of the window 220 is located at a pointsubstantially equidistant to any point on the peripheral region 261 whenviewed from the top (viewed from the radiation source). In thisembodiment, the window 220 is substantially circular in shape and thetop center region 217 corresponds to the origin of the circular window220 and any measurement of the window's diameter must pass through thetop center region 217. A bottom center region 219 of the window 220 islocated at a point substantially equidistant to any point on theperipheral region 261 when viewed from the bottom (viewed from theprocess area). In this embodiment, the window 220 is substantiallycircular in shape and the bottom center region 219 corresponds to theorigin of the circular window 220 and any measurement of the window'sdiameter must pass through the bottom center region 219. In embodimentswhere the window 220 is not circular, the top center region 217 andbottom center region 219 are located substantially in the center of theshape of the window 220.

The window 220 may be substantially symmetrical along a verticalcenterline (CL_(V)). The window 220 may also be substantiallysymmetrical along a horizontal centerline (CL_(H)). In one embodiment,the top surface 216 extends radially outward from the top center region217 to the peripheral region 261. The top surface 216 remainssubstantially linear between the top center region 217 and theperipheral region 261. In another embodiment, the bottom surface 218extends radially outward from the bottom center region 219 to theperipheral region 261. The bottom surface 218 remains substantiallylinear between the bottom center region 219 and the peripheral region261. In both embodiments, a distance between the center regions 217 and219 is less than a distance between the top surface 216 and the bottomsurface 218 at the peripheral region 261. In one embodiment, theperipheral region 261 is substantially parallel with the verticalcenterline. Thus, the window 220 exhibits a thick edge and a thincenter.

The geometric shape of the window 220 also affects the amount ofradiation that eventually reaches the substrate. The window 220 exhibitsa taper, defined as the relationship between the top surface 216 and thebottom surface 218, which increases across the window 220 from thecenter regions 217 and 219 to the peripheral region 261. The taper ofthe window 220 is related to the amount of radiation that reaches thesubstrate and may be determined by the Fresnel equation. Thus, if agreater taper of the window 220 is present, less radiation will reachthe substrate. If a lesser taper of the window 220 is exhibited, moreradiation will reach the substrate. This principle results from thephysical characteristics of light regarding the ratio of reflection(taper of the window 220) to transmission.

The angle of incidence is an important factor in adjusting the ratio ofreflection to transmission. In one embodiment, the taper is designedsuch that most of the radiation leaving a radiation source has an angleof incidence at the top surface 216 or the bottom surface 218 is notgreater than 45°. In this embodiment, the window may be formed to havean angle of incidence between about 0° to about 45° and an amount ofradiation not reflected is approximately equal to a horizontal taperangle of the window 220. If uniform intensity is present over the angleof incidence, the reflected radiation equals the taper angle/90°. Forexample, if the window 220 exhibits a 45° taper, approximately half ofthe light is reflected. The window 220 may also affect the uniformity ofthe irradiance at the substrate by altering the optical path length ofthe light. As such, the window 220 may contain characteristics of alens.

A reflective coating, such as those previously described, may bedisposed on desired surfaces of the window 220. In one embodiment, areflective coating 250 may be disposed on the top surface 216 of thewindow 220. In another embodiment, a reflective coating 251 may bedisposed on the bottom surface 218 of the window 220. In anotherembodiment, the window 220 comprises the coating 250 on the top surface216 and the coating 251 on the bottom surface 218. The reflectivecoatings 250 and 251 may be deposited by any convenient method, such asCVD, PVD, or liquid coating methods. However, the coatings 250 and 251may be deposited in such a manner that reflects the topography of thetop surface 216 and bottom surface 218 of the window 220. The thicknessof the reflective coatings 250 and 251 may be selected to increase ordecrease the amount of radiation that reaches the substrate.

In certain embodiments, an absorptive coating 260 may be disposed on theperipheral region 261. In one embodiment, the window 220 peripheralregion 260 may face a beam dump (not shown), for example, an absorbingsurface often in the form of a v-cross sectioned cavity to enhance thenet absorbance. The absorptive coating 260 comprises a material thatabsorbs radiation within a certain wavelength. Absorptive materials maybe carbon black, graphite, SiC, black chrome oxide, copper oxide, etc.The absorptivity can be further enhanced by texturing the windowsurface. Generally, the absorptive coating 260 is selected to absorbwavelengths that correspond to the pyrometer bandwidth. If the window220 comprises two reflective coatings, such as a reflective coating 250on the top surface 216 and a reflective coating 251 on the bottomsurface 218, a “hall of mirrors” effect may be produced. The “hall ofmirrors” effect results from the reflected wavelength of light beingcontinually reflected within the window 220 between the opposingreflective coatings 250 and 251. The absorptive coating 260 generallyprevents the “hall or mirrors” effect by absorbing the wavelengths ofreflected light and preventing the reflected wavelengths fromcontinually reflecting within the window 220. The geometric shape of thewindow 220 directs the reflected wavelengths toward to the absorptivecoating 260. In this way, the absorptive coating 260 may be ananti-reflective coating.

In another embodiment, the window 220 may optionally comprise an indexmatching material 290 (shown in shadow). The index matching material 290is generally selected to match the refractive index of the non-coatedportion of the window 220, although different index material withcorresponding adjusted thickness may also be used. Use of the indexmatching material 290 reduces the geometrical optic effects of thevariable thickness window 220.

FIG. 2B is a cross-sectional view of a window according to anotherembodiment of the invention. A window 225 for use in a thermalprocessing chamber, as described elsewhere herein, is provided. Thewindow 225 comprises a quartz material. The window 225 comprises a topsurface 222, a bottom surface 224, and a peripheral region 261. In oneembodiment, the top surface 222 is the side of the window 225 that facesa radiation source and the bottom surface 224 is the side of the window225 facing a processing area. A top center region 223 of the window 225is located at a point substantially equidistant to any point on theperipheral region 261 when viewed from the top (viewed from theradiation source). In this embodiment, the window 225 is substantiallycircular in shape and the top center region 223 corresponds to theorigin of the circular window 225 and any measurement of the window'sdiameter must pass through the top center region 223. In one embodiment,the bottom surface 224 is substantially planar.

In one embodiment, the window 225 is substantially symmetrical along avertical centerline (CL_(V)). In one embodiment, the top surface 222extends radially outward from the top center region 223 to theperipheral region 261. The top surface 222 remains substantially linearbetween the top center region 223 and the peripheral region 261. Inanother embodiment, the bottom surface 224 is substantially planaracross a diameter of the window 225 which passes through the top centerregion 223 between opposing points of the peripheral region 261. In bothembodiments, a distance between the center region 223 and the bottomsurface 224 is less than a distance between the top surface 222 and thebottom surface 224 at the peripheral region 261. In one embodiment, theperipheral region 261 is substantially parallel with the verticalcenterline. Thus, the window 225 exhibits a thick edge and a thincenter.

Reflective coatings 250 and 251 and an absorptive coating 260 may bedisposed on the window 225. In certain embodiments, the absorptivecoating 260 may be replaced by a beam dump as described above. Adetailed description with regard to the various coatings may be foundabove in the description related to FIG. 2A. An index matching material290 may also be disposed on the window 225. Although similar to theindex matching material 290 of FIG. 2A, the index matching material 290shown in FIG. 2B may be disposed only on the non-planar top surface 222,of the window 225. The top surface 222 may also have the reflectivecoating 250 disposed thereon. In this embodiment, the index matchingmaterial 290 may be disposed on the reflective coating 250. Similar toFIG. 2A, the area occupied by the index matching material 290 (as shownin phantom) may comprise a reflective material. In one embodiment, thethickness and topography of the reflective material may be selected toincrease or decrease the transmission of light within a selectedwavelength, such as the pyrometer bandwidth.

FIG. 2C is a cross-sectional view of a window according to anotherembodiment of the invention. A window 240 for use in a thermalprocessing chamber is provided. The window 240 comprises a quartzmaterial. The window 240 comprises a top surface 236, a bottom surface238, and a peripheral region 261. In one embodiment, the top surface 236is the side of the window 240 that faces a radiation source and thebottom surface 238 is the side of the window 240 facing a processingarea. A top center region 237 of the window 240 is located at a pointsubstantially equidistant to any point on the peripheral region 261 whenviewed from the top (viewed from the radiation source). In thisembodiment, the window 240 is substantially circular in shape and thetop center region 237 corresponds to the origin of the circular window240 and any measurement of the window's diameter must pass through thetop center region 237. A bottom center region 239 of the window 240 islocated at a point substantially equidistant to any point on theperipheral region 261 when viewed from the bottom (viewed from theprocess area). In this embodiment, the window 240 is substantiallycircular in shape and the bottom center region 239 corresponds to theorigin of the circular window 240 and any measurement of the window'sdiameter must pass through the bottom center region 239.

In one embodiment, the window 240 is substantially symmetrical along avertical centerline (CL_(V)). In another embodiment, the window 240 issubstantially symmetrical along a horizontal centerline (CL_(H)). In oneembodiment, the top surface 236 extends radially outward from the topcenter region 237 to the peripheral region 261. The top surface 236exhibits non-linear characteristics between the top center region 237and the peripheral region 261. In another embodiment, the bottom surface238 extends radially outward from the bottom center region 239 to theperipheral region 261. The bottom surface 238 exhibits non-linearcharacteristics between the bottom center region 239 and the peripheralregion 261. In both embodiments, a distance between the center regions237 and 239 is less than a distance between the top surface 236 and thebottom surface 238 at the peripheral region 261. In one embodiment, theperipheral region 261 is substantially parallel with the verticalcenterline. Thus, the window 220 exhibits a thick edge and a thincenter. The top surface 236 and bottom surface 238 are oriented suchthat the geometry of the window 240 is similar to a concave lens.

Reflective coatings 250 and 251 and an absorptive coating 260 may bedisposed on the window 240. A detailed description with regard to thevarious coatings may be found above in the description related to FIG.2A. An index matching material 290 may also be disposed on the window240. Similar to the index matching material 290 of FIG. 2A, the indexmatching material 290 shown in FIG. 2C may be disposed above the topsurface 236 of the window 240 and below the bottom surface 238 of thewindow 240. Similar to FIG. 2A, the area occupied by the index matchingmaterial 290 (as shown in phantom) may comprise a reflective material.In one embodiment, the thickness and topography of the reflectivematerial may be selected to increase or decrease the transmission oflight within a selected wavelength, such as the pyrometer bandwidth.

FIG. 2D is a cross-sectional view of a window according to oneembodiment of the invention. In one embodiment, a first window 230 and asecond window 235 are provided. Together, the windows 230 and 235 form asingle window for use in a thermal processing chamber. The windows 230and 235 comprise a quartz material. The first window 230 comprises a topsurface 227, a bottom surface 226, and a first peripheral region 228. Inone embodiment, the top surface 227 is adjacent to the second window 235and the bottom surface 226 is the side of the window 225 facing aprocessing area. The top surface 227 extends across the diameter of thefirst window 230 in a linearly diagonal fashion from the firstperipheral region 228 to the bottom surface 226 of the first window 230.The first peripheral region 228 is substantially perpendicular to thebottom surface 226. As depicted in the cross-sectional view, the firstwindow 230 resembles a right triangle wherein the top surface 227 formsthe hypotenuse of the cross-sectional right triangle.

In certain embodiments, the first window 230 further comprisesreflective coatings 250 and 251 and an absorptive coating 260. Thereflective coating 250 is disposed on the top surface 227 and thereflective coating 251 is disposed on the bottom surface 226 of thefirst window 230. The absorptive coating 260 is disposed on the firstperipheral region 228. Further description regarding the materials usedfor the reflective coatings 150 and 151 and the absorptive coating 260are not discussed here for the sake of brevity but may be found withreference to FIG. 2A.

In another embodiment, the second window 235 comprises a top surface234, a bottom surface 233, and a second peripheral region 232. In oneembodiment, the bottom surface 233 is adjacent to the first window 230and the top surface 234 is the side of the window 235 facing a radiationsource. The bottom surface 233 extends across the diameter of the secondwindow 235 in a linearly diagonal fashion from the first peripheralregion 228 of the first window 230 to the second peripheral region 232of the second window 235. The second peripheral region 232 issubstantially perpendicular to the top surface 234. As depicted in thecross-sectional view, the second window 235 resembles a right trianglewherein the bottom surface 233 forms the hypotenuse of thecross-sectional right triangle.

In one embodiment, the bottom surface 233 of the second window 235 isdisposed immediately adjacent the reflective coating 250 formed on thetop surface 227 of the first window 230. The first window 230 and thesecond window 235 “sandwich” the reflective layer 250 so that no spaceor void is present between the two windows and the reflective layer 250.This is done so as to reduce the number or mediums through whichradiation must travel in an effort to prevent unnecessary loss ofradiation due to the refractive indicies of multiple media. Although notshown, it is contemplated that, in certain embodiments, the reflectivecoating 251 may be formed on the top surface 234 of the second window235. In this embodiment, the reflective coating may be formed on thebottom surface 233 of the second window 235 and the absorptive coating260 may be formed on the second peripheral region 232 of the secondwindow 235. Furthermore, all non-peripheral surfaces 234, 233, and 226may be coated by the absorptive coating 260.

An example of an RTP chamber that may use or include embodimentsdescribed herein is the RADIANCE® RTP chamber available from AppliedMaterials, Inc., of Santa Clara, Calif. RTP chamber from othermanufacturers may also benefit from use of embodiments described herein.It will be understood that in the Figures described above, the radiationsource is positioned above the substrate and the pyrometer is positionedbelow the radiation source and the substrate. The substrate may also bedisposed upside down within the chamber. Other configurations of theprocessing chamber with varying window geometries are possible and arefully contemplated and within the scope of the invention. For instance,a processing chamber may have a radiation source below a substrate and apyrometer positioned above a radiation source. These and othervariations of positioning of the substrate, radiation source, andpyrometer are possible and are contemplated without fundamentallyaffecting aspects of the invention described herein.

While the foregoing is directed to embodiments of the invention, otherand further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

The invention claimed is:
 1. A thermal processing apparatus, comprising:a window comprising quartz having a plurality of surfaces including atop surface and a bottom surface, the window having a geometric shape,wherein a thickness of the window at a center region is less than athickness of the window at a peripheral region, and wherein the topsurface tapers inwardly from the peripheral region to the center region;a reflective coating disposed on the top surface and the bottom surface;an index matching material disposed on the reflective coating adjacentthe top surface; and an absorptive coating disposed on the peripheralregion.
 2. The apparatus of claim 1, wherein the index matching materialis selected in relationship to a refractive index of the window.
 3. Theapparatus of claim 2, wherein the reflective coating is selected toreflect a predetermined range of wavelengths between about 700 nm toabout 1000 nm.
 4. The apparatus of claim 1, wherein the reflectivecoating comprises a dielectric material.
 5. The apparatus of claim 4,wherein the dielectric material comprises multiple layers.
 6. Theapparatus of claim 1, wherein the window is symmetric around a verticalaxis.
 7. The apparatus of claim 6, wherein the window is asymmetricaround a horizontal axis.
 8. The apparatus of claim 1, wherein theplurality of surfaces are linear.
 9. A system for processing asubstrate, comprising: a radiation source; a pyrometer; and a windowcomprising quartz disposed between the radiation source and thepyrometer, the window further comprising: a plurality of surfacesincluding a top surface and a bottom surface, the window having ageometric shape, wherein a thickness of the window at a center region isless than a thickness of the window at a peripheral region, and whereinthe top surface tapers inwardly from the peripheral region to the centerregion; a reflective coating disposed on the top surface and the bottomsurface; an index matching material disposed on the reflective coatingadjacent the top surface; and an absorptive coating disposed on theperipheral region.
 10. The system of claim 9, wherein the pyrometerdetects wavelengths between about 700 nm to about 1000 nm.
 11. Thesystem of claim 9, wherein the index matching material is selected inrelationship to a refractive index of the window.
 12. The apparatus ofclaim 11, wherein the reflective coating is selected to reflect apredetermined range of wavelengths between about 700 nm to about 1000nm.
 13. The apparatus of claim 9, wherein the reflective coatingcomprises a dielectric material.
 14. The apparatus of claim 9, whereinthe window is symmetric around a vertical axis.
 15. The apparatus ofclaim 14, wherein the window is asymmetric around a horizontal axis. 16.The apparatus of claim 9, wherein the plurality of surfaces are linear.17. A thermal processing apparatus, comprising: a window having aplurality of surfaces including a top surface and a bottom surface, thewindow having a geometric shape, wherein a thickness of the window at acenter region is less than a thickness of the window at a peripheralregion, and wherein the top surface tapers inwardly from the peripheralregion to the center region; a reflective coating disposed on the topsurface and the bottom surface; and an absorptive coating disposed onthe peripheral region.